1. Field of the Invention
The present invention relates to a recording apparatus of a digital video signal, a reproducing apparatus thereof, and a recording method thereof for use with a digital VCR that compresses the digital video signal by a DCT circuit and records the compressed digital video signal on a magnetic tape by a rotating head.
2. Description of the Prior Art
Digital VCRs that convert a digital video signal into a signal with a frequency range by a DCT (Discrete Cosine Transform) circuit, compress the converted signal by variable length code encoding circuit, and record the compressed signal on a magnetic tape by a rotating head have been developed. FIG. 1 shows the construction of a recording system of such a conventional digital VCR. In this example, a video signal corresponding to the conventional television system such as the NTSC-system, PAL system, or the like is recorded corresponding to a component system.
In FIG. 1, reference numeral 101 is an input terminal of a luminance signal Y. Reference numerals 102 and 103 are input terminals of color difference signals R-Y and B-Y, respectively. Reference numeral 104 is an A/D converter that converts the analog luminance signal into a digital signal. Reference numeral 105 is an A/D converter that converts the analog color difference signals R-Y and B-Y into respective digital signals. The luminance signal received from the input terminal 101 is supplied to the A/D converter 104. The A/D converter 104 converts the luminance signal into a digital signal with a sampling frequency of 13.5 MHz. The color difference signals R-Y and B-Y received from the input terminals 102 and 103 are supplied to the A/D converter 105. The A/D converter 105 converts the color difference signals R-Y and B-Y into respective digital signals with a sampling frequency of 6.75 MHz. Thus, so-called (4, 2, 2) component video signals, where the relation of information amounts of luminance signal Y, and color difference signals U and V is 4:2:2, are input.
Reference numeral 106 is a thin-out and line sequencing circuit. The thin-out and line sequencing circuit 106 halves samples of the color difference signals R-Y and B-Y converted by the A/D converter 105 in vertical direction and arranges the color difference signals R-Y and B-Y in line sequence. Thus, so-called 4:2:0 sampling construction takes place.
Reference numeral 107 is a block segmenting and shuffling circuit. The block segmenting and shuffling circuit 107 shuffles the digital signals as so-called macro-blocks. One DCT block, which is a unit of DCT operation, is composed of eight pixels in the horizontal direction times eight pixels in the vertical direction. One macro-block is composed of four DCT blocks of a luminance signal, one DCT block of a corresponding R-Y signal, one DCT block of a corresponding B-Y signal construct one DCT block, namely a total of six macro-blocks. The macro-blocks are shuffled so as to equally compress the entire image.
Reference numeral 108 is a DCT circuit. Reference numeral 109 is a buffer circuit. Reference 110 is a quantizing circuit. Reference numeral 111 is an estimator. An output of the block segmenting and shuffling circuit 107 is supplied to the DCT circuit 108. The DCT circuit 108 transforms sample data, composed of eight pixels in the horizontal direction times eight pixels in the vertical direction, into data with a frequency range corresponding to two-dimensional discrete cosine transform technique. The resultant data is supplied to both the buffer 109 and the estimator 111.
The buffer 109 has a fixed buffer amount. In this case, the buffer amount of the buffer 109 is equivalent to five macro-blocks (namely, five sync blocks). The estimator 111 estimates the code amount of the fixed buffer amount of data that a particular quantizes into a variable length code and selects an optimum quantizing table so that the fixed buffer amount becomes equal to or less than the predetermined code amount.
The quantizer 110 has various quantizing tables. The estimator 111 selects an optimum quantizing table so that the total code amount of the buffer amount becomes equal to or less than the predetermined amount. The DCT data stored in the buffer 109 is quantized by the quantizer 110.
Reference numeral 112 is a variable length code encoding circuit. The variable length code encoding circuit 112 encodes data into a variable length code such as a two-dimensional Huffman code.
Reference numeral 113 is a frame segmenting circuit. The frame segmenting circuit 113 places a predetermined pattern sync at the beginning of the record data so as to perform an error correction code encoding process and develop the record data into frames. An output of the variable length code encoding circuit 112 is supplied to the frame segmenting circuit 113. In this example, data of one macro-block is allocated to one sync block.
Reference numeral 114 is a channel encoder. Frame-segmented data is supplied to the channel encoder 114. The channel encoder 114 modulates the frame segmented data corresponding to a predetermined modulation system. An output of the channel encoder 114 is supplied to rotating heads 116A and 116B through recording amplifiers 115A and 115B, respectively. The rotating heads 116A and 116B record compressed video signals on a magnetic tape (not shown).
The rotating heads 116A and 116B have different azimuth angles. A rotating drum is rotated at 150 Hz. Thus, when a video signal of the NTSC system with a field frequency of 60 Hz is recorded, the number of tracks per frame is 10. On the other hand, when a video signal of the PAL system with a field frequency of 50 Hz is recorded, the number of tracks per frame is 12.
In the above-described prior art reference, a video signal of a conventional television system such as the NTSC system, the PAL system, or the like is recorded through the DCT process and the variable length code encoding process. A system for allowing such a digital VCR to further record a HDTV (High Definition Television) signal has been proposed. When a video signal of the conventional television system is recorded, the two rotating heads 116A and 116B are used. However, to record a HDTV signal, four rotating heads should be disposed on a rotating drum. When the HDTV signal is recorded, the tape running speed should be twice as high as that of the conventional television system.
When the HDTV signal is recorded, the operation speed of the digital VCR should be raised so as to process the HDTV signal with a high transmission rate. If the video signal recording circuit used for the conventional NTSC system and the PAL system is used in common with the HDTV system, the circuit scale of the VCR can be reduced.
In addition, such a digital VCR is required to be reproduced in variable speed reproduction mode with high picture quality. Thus, when a HDTV signal is recorded by such a digital VCR, data assignment on tracks should be considered so that good picture quality can be obtained in the variable speed reproduction mode.